This invention relates to electromechanical systems, and more particularly to micro-electromechanical systems (MEMS) and operating methods therefor.
Micro-electromechanical systems (MEMS) have been developed as alternatives to conventional electromechanical devices, such as relays, actuators, valves and sensors. MEMS devices are potentially low-cost devices, due to the use of micro-electronic fabrication techniques. New functionality also may be provided, because MEMS devices can be much smaller than conventional electromechanical devices.
Many applications of MEMS technology use MEMS actuators. These actuators may use, for example, one or more beams that are fixed at one or both ends. These actuators may be actuated electrostatically, magnetically, thermally and/or using other forms of energy.
A major breakthrough in MEMS actuators is described in U.S. Pat. No. 5,909,078 entitled Thermal Arched Beam Micro-electromechanical Actuators. Disclosed is a family of thermal arched beam micro-electromechanical actuators that include an arched beam which extends between spaced apart supports on a micro-electronic substrate. The arched beam expands upon application of heat thereto. Thermal arched beam micro-electromechanical devices and associated fabrication methods also are described in U.S. Pat. No. 5,955,817 to Dhuler et al. entitled Thermal Arched Beam Micro-electromechanical Switching Array; U.S. Pat. No. 5,962,949 to Dhuler et al. entitled Micro-electromechanical Positioning Apparatus; U.S. Pat. No. 5,994,816 to Dhuler et al. entitled Thermal Arched Beam Micro-electromechanical Devices and Associated Fabrication Methods; U.S. Pat. No. 6,023,121 to Dhuler et al. entitled Thermal Arched Beam Micro-electromechanical Structure.
MEMS actuators may be utilized in a variety of optical components. For example, various circuits utilize MEMS mirrors which may utilize actuators in order to adjust the tilt of the mirrors. Such tiltable MEMS mirrors may be used, for example, in optical transmission circuits. MEMS mirrors typically are also provided with suspension springs which introduce mechanical resistance during movement of the mirrors to adjust tilt. In addition, damping means, such as squeeze film (air) damping or active servo control, are generally provided to aid in damping shock or vibration of the mirrors. Such approaches typically are only applicable for frequencies below the harmonic frequency of the mirror system.
Unfortunately, conventional MEMS actuators may require continuous application of an electrostatic potential, a magnetic field, electric current and/or other energy to the MEMS actuator in order to maintain the actuator in a set or actuated position. This may consume excessive power. Moreover, an interruption of power may cause the actuator to reset.
It is known to provide notches, dimples, protrusions, indentations and/or other mechanical features in MEMS actuators that can allow the actuator to be mechanically set in a given position. See for example, the above-cited U.S. Pat. No. 5,955,817 and 5,994,816. Unfortunately, these mechanical features may be subject to wear. Moreover, mechanical locking that relies on friction may be difficult to obtain reliably due to the small dimensions of MEMS actuators and the uncertain values of static and dynamic friction in MEMS devices. Thus, notwithstanding conventional micro-electromechanical devices, there continues to be a need for lockable micro-electromechanical actuators that need not consume power when locked and need not rely on mechanical friction for locking.
Mounting systems for micro-electromechanical system (MEMS) structures according to embodiments of the invention include a non-Newtonian fluid having a threshold viscosity that is positioned between a MEMS base member and the MEMS structure so as to position the MEMS structure relative to the base member. A MEMS actuator is coupled to the MEMS structure. The MEMS actuator is positioned to cause movement of the MEMS structure relative to the MEMS base member by generating a force sufficient to exceed the threshold viscosity of the non-Newtonian fluid when the MEMS actuator is activated.
The non-Newtonian fluid may be coupled to the MEMS structure by fluid tension. The non-Newtonian fluid may have an associated viscosity, when the MEMS actuator is not activated, selected to latch the MEMS structure in a desired position and dampen motion of the MEMS structure. The non-Newtonian fluid may be a magnetorheological (MR) fluid, an electrorheological (ER) fluid or a grease.
In further embodiments of the present invention, the MEMS actuator is an electromagnetic actuator. The electromagnetic actuator includes a coil member connected to either the MEMS structure or the MEMS base member and a passive member connected to the other of the MEMS structure and the MEMS base member. The passive member is positioned adjacent the coil member so as to be either attracted to or repelled from the coil member when the coil member is activated by passing an electrical signal therethrough. The passive member may be a magnetic plate connected to the MEMS structure and the coil member may be a planar coil fabricated on the MEMS base member.
In other embodiments of the present invention, a bearing member is positioned between the MEMS base member and the MEMS structure that movably couples the MEMS structure to the MEMS base member. The non-Newtonian fluid suspends the MEMS structure relative to the MEMS base member. The bearing member may pivotally couple the MEMS structure to the base member and the actuator may be positioned to cause pivotal movement of the MEMS structure about the bearing member when the actuator is activated. The non-Newtonian fluid may be located at a position displaced from the bearing member and the actuator may be positioned on the same side of the bearing member as the non-Newtonian fluid. The actuator may be positioned at substantially the same location between the MEMS structure and the base member as the non-Newtonian fluid.
In yet further embodiments of the present invention, the non-Newtonian fluid is a magnetorheological (MR) fluid and the actuator is an electromagnetic actuator. The electromagnetic actuator includes a coil member connected to either the MEMS structure or the MEMS base member and a passive member connected to the other of the MEMS structure and the MEMS base member. The passive member may be positioned adjacent the coil member so as to be either attracted to or repelled from the coil member when the coil member is activated by passing an electrical signal therethrough. The coil member may be further configured to generate trim fields that buck a magnetic field extending into the MR fluid so that the MR fluid will convert to a Newtonian flow state. The coil member may then further rotate the MEMS structure about the bearing member when the coil member is activated. The passive member may be a magnetic member that generates the magnetic field extending into the MR fluid. Alternatively, an external magnet may be positioned adjacent the suspension system to generate the magnetic field extending into the MR fluid.
In other embodiments of the present invention, an electrical connection is provided to the MEMS structure. The non-Newtonian fluid in such embodiments is a electrorheological (ER) fluid and the actuator is an electromagnetic actuator. The electromagnetic actuator includes a coil member connected to either the MEMS structure and the MEMS base member and a passive member connected to the other of the MEMS structure and the MEMS base member. The passive member is positioned adjacent the coil member so as to be either attracted to or repelled from the coil member when the coil member is activated by passing an electrical signal including a magnetic field signal, that provides a magnetic field that results in the magnetic member being either attracted to or repelled from the coil member, and an electrical field signal thereto. The electrical field signal provides an electrical field between the MEMS structure and the coil member using the electrical connection to the MEMS structure, the electrical field maintaining the non-Newtonian fluid in a non-Newtonian state when the electrical field signal is activated.
In further embodiments of the present invention, a second non-Newtonian fluid is positioned between the base member and the MEMS structure at a second position displaced from the bearing member in a direction opposite from the position of the first non-Newtonian fluid. A second actuator is positioned on the same side of the bearing member as the second non-Newtonian fluid so as to cause pivotal movement of the MEMS structure about the bearing member by generating a force sufficient to exceed the threshold viscosity of the second non-Newtonian fluid when the second actuator is activated.
In other embodiments of the present invention, a micro-electromechanical system (MEMS) mirror apparatus is provided including a MEMS substrate and a MEMS mirror adjacent the substrate. A joint is positioned between the substrate and the MEMS mirror that pivotally couples the MEMS mirror and the substrate. A non-Newtonian fluid having a threshold viscosity is positioned between the substrate and the MEMS mirror that suspends the MEMS mirror relative to the substrate. A MEMS force generator is coupled to the MEMS mirror at a position displaced from the joint that is configured to generate a force sufficient to overcome the threshold viscosity of the non-Newtonian fluid so as to cause pivotal movement of the MEMS mirror about the joint.
The MEMS mirror may be suspended from the MEMS substrate without the use of suspension springs. The joint may be a solder bump on the MEMS substrate and the MEMS mirror may include an etch pit on a surface thereof configured to rotatably receive the solder bump. The threshold viscosity of the non-Newtonian fluid may be from about 1 centipoise (cP) to about 1000 cP, and may further be from about 10 cP to about 100 cP.
In yet other embodiments of the present invention, methods are provided for controlling a position of a MEMS structure suspended from a MEMS substrate by a non-Newtonian fluid for pivotal movement about a joint. The method includes estimating a position of the MEMS structure and determining a desired movement direction based on the estimated position and a desired position. A MEMS force generator is activated to generate a force in a desired direction and having a magnitude sufficient to overcome a threshold viscosity of the non-Newtonian fluid. The desired direction corresponds to the determined desired movement direction. The MEMS force generator is deactivated when the position of the MEMS structure corresponds to the desired position.
In further method embodiments of the present invention, the non-Newtonian fluid is an electrorheological (ER) fluid and the MEMS force generator includes a passive member and a coil member connected to respective ones of the MEMS structure and the MEMS substrate and positioned substantially at a same location between the MEMS structure and the MEMS substrate as the non-Newtonian fluid. In such embodiments, activating the MEMS force generator includes deactivating an electrical field between the coil member and the MEMS structure so that the non-Newtonian fluid will convert to a Newtonian flow state. A magnetic field between the coil member and the passive member is activated to generate the force in the desired direction to pivot the MEMS structure about the joint while the electrical field is deactivated. The electrical field is activated to return the non-Newtonian fluid to a non-Newtonian flow state after the MEMS structure has pivoted to the desired position. The magnetic field is deactivated after the MEMS structure has pivoted to the desired position.